The invention relates to a safety arrester for arresting a hydraulically operated lifting ram of a hydraulic elevator.
In many instances hydraulic lifting rams require safety devices to prevent the ram, when extended, from collapsing when there is a sudden fall in hydraulic pressure due to a fault. In the absence of any safety measures such a fault could be extremely hazardous, since it could cause a passenger cage or a lifting platform to fall.
Arrester devices have already been proposed which respond to excessive ram speed. However, the connection between a release lever of the known arrester device and a control line attached to the lever are a particular source of weakness. Particularly when maintenance and assembly have been careless, the failure of this arrangement may cause the entire arrester device to fail. Moreover, in hydraulic lifting installations the provision of an automatically closing safety valve has also been proposed for isolating the lifting cylinder and thereby preventing the ram from continuing to descend when a pipe fracture has occured and the pressure suddenly and undesirably falls for this or some other reason. Such a safety arrangement does not have a satisfactory all-round protective effect because the results of a leakage in the lifting cylinder itself cannot be controlled by the closure of such a valve.
Brake means which comprise band-like elements embracing the ram are also known, as are brake means comprising a wedge member controlled by hydraulic pressure and cooperating with one side of the ram. None of the known forms of construction provides full protection and safety in every circumstance that may arise.